Open-loop apparatus for producing a controlled blend of polyol and blowing agent for use in the manufacture of polyurethane foam

ABSTRACT

A novel apparatus has been discovered which is of value in the production of polyurethane foam. This invention relates to a one-pass, on-demand apparatus for producing a controlled, homogeneous blend of the polyol-blowing agent mixture used in the manufacture of polyurethane foam using either a low-boiling point or high-boiling point blowing agent. An apparatus is provided to control the amount of each material in the mixture, ensure homogeneous blending of the two materials after mixing, a pressure control means to maintain blowing agents in their liquid state (where necessary), and a monitoring means which allows rapid verification of the operating status of the entire system.

This application is a division of application Ser. No. 08/691,510 filedAug. 2, 1996, now U.S. Pat. No. 5,958,991, which is incorporated byreference.

FIELD OF THE INVENTION

This invention relates to the production of polyurethane foams, and moreparticularly, to an apparatus for mixing certain polyurethane precursormaterials in an open-loop, single pass, processing system, whicheliminates the need for a mixing tank (e.g. a mixer with storagecapicity).

BACKGROUND OF THE INVENTION

Historically, the manufacture of rigid foamed polyurethanes hastypically included the use of various combinations of a polyol,isocyanate, water, and trichlorofluoromethane (CFC-11) as a foaming orblowing agent. Traditionally, the materials were mixed together in astep-wise process. The polyol provided the polymer component which, whenreacted with isocyanate, would polymerize and harden. Both polyol andisocyanate are liquid materials. The blowing agents traditionally used,such as CFC-11, are also liquid at room temperature but upon heating orundergoing rapid pressure reduction will volatilize. The addition of ablowing agent during the mixture process will create gaseous expansionupon either temperature elevation or pressure reduction within thepolymerizing polyol matrix thereby causing the polyol to foam. Foamedpolyurethanes have good mechanical and thermal insulating properties andshow excellent dimensional stability, and chemical resistance. Thefoaming process allows the polyurethane to expand to fill a void definedby a formed structure such as a refrigerator door or body panel.Polyurethane foams are widely used as thermal insulating materials forhome appliances, truck trailers and railroad cars, insulated storagevessels, building materials, and certain parts for automobiles.

It is well known in the art of foam production that use of liquidblowing agents is highly desirable. The reason is that foaming of thepolyol is desired to occur as a final step in the process as thereactants are added to their mold. Generally, the blowing agent is addedto polyol and mixed, then the blended mixture is subsequently added toisocyanate just prior to injection into a mold. Concerning the mixtureof polyol to blowing agent, it has been common practice in thoseindustries making polyurethane foams to use batch mixing processtechniques to mix large volumes because of the relative insolubility ofsome common blowing agents with polyol. In batch mixing, the blowingagent is added to the foam polymer (preferably polyol) and continuouslymixed by recirculating the mixture through a mixing reservoir over alengthy period of time resulting, eventually, in a batch of mixed or,“blended,” polyol and blowing agent. The time of mixing is directlyrelated to the volume being mixed and the degree of difficulty ofsolubilizing the blowing agent into the polyol. Once the desired ratioof blowing agent and polyol was obtained and the materials thoroughlymixed, the process could be allowed to proceed to the polymerization andfoaming steps by the addition of isocyanate and reduction of pressure orelevation of temperature. One aspect of realizing the solubility of someblowing agents with polyol was the necessity of keeping the blowingagent/polyol mix under constant high partial pressure of either an inertgas, such as nitrogen, or causing supersaturated conditions by pumpingexcess blowing agent into the mixing tank, the tank being kept in aclosed loop isolated from and elevated relative to atmospheric pressure.For economic reasons, practitioners typically desired to make largequantity batches mixed well in advance of their needed use. The advancemixing and subsequent storage over a relatively long period of timeallowed the use of common quality control techniques, such as samplingand weighing, to test the blended material and ensure compliance withspecifications. Much of the mixing techniques were carried out on atrial and error basis. One significant problem of such mixing processeshas been the retention of some blowing agents dispersed in the polyol.If, prior to use, the batches were found to be out of specification, themixtures were reprocessed by adding the amounts of the variouscomponents to bring the blend within desired specifications. Thisprocess required remixing of the reagents with materials being routedback to mixing chambers. Such processes are inefficient, cumbersome andrequire additional and expensive equipment.

The prior art offers numerous examples of attempts at advancing the artof making polyurethane foam. Critical to the formation of foam is theamount and homogeneity of dissolved blowing agent. Properties of thequality of the foam will vary greatly depending on the amount,dispersion, and type of the blowing agent used. The present inventionprovides for an apparatus in which polyol and blowing agent may be mixedunder highly controlled pressure levels and flow rates. A significantadvantage of the present invention over prior art is the elimination ofa need for batch mixing and the ability to monitor and control preciselyboth the amounts of reagents added together and the mixing thereof. Thepresent invention allows for predetermination of all essentialparameters of the materials used in the process of creating blendedpolyol giving reproducibility, predictability, and consistency in thefoam formed from the blended polyol prepared by the present invention.

The present invention is patentably distinguishable from previousimprovements in numerous respects. For example, U.S. Pat. No. 4,132,838entitled, Process and Apparatus for the Preparation of a ReactionMixture for the Production of Plastic Foams, by K. D. Kreuer et al.,discloses an apparatus designed to obtain better control of mixingblowing gases with one of the reagents in order to achieve predictablehomogeneity in the polyol/gas mixture. Kreuer's apparatus essentiallycontrolled the velocity of flow rates of one of the reaction reagentsinto which a gas blowing agent was aspirated. Unlike the presentinvention which maintains the blowing agent in the liquid phase,Kreuer's device contemplated use of a vapor phase blowing agent, theaddition of which to polyol was not under strict user control. Moreover,one embodiment of the Kreur system required return flow to a batchmixing chamber. Likewise, U.S. Pat. No. 4,157,427 entitled, Method forEntraining Gas in a Liquid Chemical Precursor for Reaction InjectionMolding, by G. Ferber, disclosed an improvement in sampling the amountof vapor phase blowing agent infused into one of the reactioncomponents. However, like other examples of the prior art, the apparatuscontemplated recirculation of the reactant/gas mixture to a batch mixingchamber.

Various other improvements are found in the prior art which concern themixing of a gas blowing agent. U.S. Pat. No. 4,288,230 entitled Methodand a Device for the Production of a Solid-Forming or Foam-FormingFlowable Reaction Mixture, by W. Ebeling and V. Tennemann discloseddetermining gas infusion by measuring quantitative flow rates of gas bytaking density readings against volumetric flow. This device merelyadded gas and recirculated the gas/polyol mixture until the desired mixwas obtained as determined by taking density and volumetric flowreadings. In U.S. Pat. No. 4,376,172 entitled Closed Loop Control ofCompressible Fluid Addition to a Mixture of such Fluid and a Liquid, byG. Belangee et al., a recirculation type system is disclosed that uses aplunger to measure the amount of gas blowing agent to be infused.

In U.S. Pat. No. 4,526,907 entitled Process and Device for thePreparation of a Reaction Mixture of at Least Two Components for theProduction of Foams, by H. Thiele et al., another method of infusing gasblowing agent is disclosed for use in a closed loop system. Otherpatents such as, U.S. Pat. No. 4,933,115 entitled Process for theProduction of a Flowable Mixture which Reacts to Form Foam from FlowableComponents Stored in Storage Containers, by K. Krippl, and U.S. Pat. No.5,000,882 entitled Apparatus for the Preparation of a Free-FlowingMixture of Free-Flowing Components which Reacts to Form Foam, by F.Proksa, et al., disclose variations on the methodology of eitheraddition of the blowing agent or the measurement thereof.

In addition to advances made in the art of infusing blowing agents, theart of foam production has had to make adjustments in the use ofchemicals and gases for environmental and safety reasons. Based ontheories that CFC compounds, particularly Freon, contribute todestruction of the protective ozone layer in the atmosphere, legislationhas been passed in many countries regulating and/or prohibiting themanufacture or use of the traditional materials used as polyurethaneblowing agents. The Clean Air Act of 1990 placed deadlines andrestrictions on the use and manufacture of all CFC compounds. Compliancewith legal restrictions requires the use of new methods and materials inthe production of polyurethane foams, particularly regarding new blowingagents. Consequently a compelling need has arisen for new processeswhich will allow flexibility in selection of the blowing agent for themanufacture of polyurethane foams.

The polyurethane foam industry is in a state of transition. Traditionalblowing agents have typically had relatively high boiling points witheasily manipulated volatility making them relatively easy to use, mix,and store in the polyurethane production process. For example, CFC-11 orFreon, has a boiling point of approximately 75 degrees F at atmosphericpressure. The environmentally friendly blowing agents coming into usebecause of the recent legislation have not been so easy to use becauseof low boiling points and high volatility. For example, 1,1,1,2tetrafluoroethane (HFC-134a) has a boiling point of approximately minus15 degrees F. Moreover, some high boiling agents have exhibited lowvolatility requiring input of heat energy into the reaction process.Other blowing agents with very low boiling points have often exhibitedproperties which made their use problematic. For instance,hydrochloroflurocarbons have been shown generally to exhibit rapidvaporization giving rise to difficulty in keeping the material insolution during batch mixing as well as causing cooling of the reactantmixture with subsequent loss of expansion capacity during foamformation. Production equipment able to accommodate such new materialswill require the ability to use blowing agents that have either a low orhigh boiling point. For example, Allied Signal manufactures more than 15compounds, classified as refrigerants, with boiling points ranging fromminus 126 to 117 degrees F, several of which have potential use asblowing agents. Moreover, the new processes will require equipment ableto mix and blend components more quickly and more accurately than thebatch mixing processes of the prior art. Where the process is to beadapted to existing polyurethane production systems, the new processesshould be able to operate effectively with minimum redesign to existingsystems.

Advancements in the art have begun to address these environmentallyrelated problems. U.S. Pat. No. 5,055,272 entitled, Method for ProducingPolyurethane Foam and Apparatus Therefor, by R. Wheeler et al.,discloses an apparatus which is designed to use non-fluorocarbon gasesand is also a single flow through system. However, unlike the presentinvention, Wheeler's device uses an expandable bladder that ispressurized by vapor phase gas and acts to maintain pressure for the gasas it is pumped into the liquid polyol. This type of device differsmarkedly from the present invention not only because of its use of vaporphase blowing agent, but also for the fact that the pressure within thesystem cannot bc accurately maintained due to the constant motion ofcontraction and expansion of the pump bladder. Thus, pressures in thesystem are continuously in flux rather than able to be maintained at aconstant value. In U.S. Pat. No. 5,472,990 entitled Method and Apparatusfor Nucleation of Polyurethane Foam which Results in Self-AdheringMicrocellular Foam, by T. Craig et al., a single pass system ispresented which is designed for using air as the blowing agent which ispumped into the polyol to create bubbles like the aforementioned art.The design of this system also relies on only one metering pump to passthe liquid reactants through the apparatus. Such a system makes accuratecontrol of the quantities of each reactant difficult. In anotherexample, U.S. Pat. No. 5,252,625 entitled Method for Producing RigidFoams and Products Produced Therefrom, by A. McLaughlin, a device isdisclosed which is able to utilize various blowing compounds but itincorporates a preblend mixing tank which also only uses a static mixerto infuse the gas with liquid component. Like the earlier batch mixapparatuses, there is little accuracy or control over the retention ofblowing agent in the liquid phase or the measurement thereof. Finally,U.S. Pat. No. 5,444,100 entitled Method for the Mixing of Low-BoilingFoaming Agent, by M. Takezawa, discloses an apparatus designed to useenvironmentally safe blowing agents but the machine is specificallydesigned only to handle low-boiling point blowing agents. Moreover, justlike the earlier prior art processes, this apparatus requires arecirculation gas/polyol mix tank.

The present invention addresses the drawbacks of previous advancementsin the art by eliminating the need for recirculation batch mixing byproviding an open-loop, single pass, “on demand” system, that is, aprocess system that can accurately mix and blend specified amounts ofliquid reagents (polyol and liquified blowing agent), monitor theamounts of each reactant before and after blending, and present theblended mixture with known composition directly to a foaming extrusionhead (e.g. no remixing tank is necessary) or to a day use tank storageunder conditions which will allow maintenance of known reactant ratios.Because of the high degree of versatility in the manner in whichreaction components may be added and monitored, the present inventionalso addresses the difficulties associated with legislative requirementsby allowing various types of environmentally-friendly chemical blowingagents to be employed. Moreover, the versatility allows the device thecapacity for accommodating both high and low-boiling point blowingagents. Concerning low boiling point blowing agents, a preferredembodiment of the present invention is use of 1,1,1,2 tetrafluoroethane(HFC-134a). This compound is known to be highly insoluble in polyol andhas been used by others wherein a solubilizing agent, such as dimethylether (DME) was necessary (U.S. Pat. No. 5,409,962 entitledSubstantially Constant Boiling Blowing Agent Compositions of 1,1,1,2Tetrafluorothane and Dimethyl Ether by P. L. Bartlett and J. A. Creazzo)to cause acceptable solubilization of the HFC-134a in the polyol. It isknown that very small amounts of some solubilizing agents, such as DME,can have dramatic effects on enhancing the solubility of such compoundsas HFC-134a in polyol. However, use of such solubilizing agents maycause problems with the polymerization process and the use of suchagents therefore should be avoided where possible. A major advantage anda preferred embodiment of the current invention is the ability ofsolubilizing HFC-134a into polyol in a pure form without the need forany solubilizing substance.

SUMMARY OF THE INVENTION

A novel apparatus has been discovered which is of value in theproduction of polyurethane foam. Specifically, the present invention isdirected to an apparatus by which the polyol and blowing agentcomponents of polyurethane are continuously and accurately mixed andblended without the necessity of recirculating the blend through aclosed-loop, batch tank process. One object of the present invention isthe ability of the apparatus to use a variety of known blowing agents.Other objects of the invention are the ability to control the amount ofeach material in the blended polyol mixture, to ensure homogeneousblending of materials after mixing, to maintain control of pressure ofthe blowing agents to assure that they remain in their liquid state(where necessary) prior to foaming, and to provide monitoring meansallowing rapid verification of the operating status of the entiresystem.

A primary object of the current invention is to provide a single pass,“on demand” apparatus which is able to maintain the blowing agent in aliquid state with tight control over pressures, flow rates, and/ortemperatures at which blending and mixing takes place, and in whichaccurate control of blowing agent to polyol reactant ratios aremaintained. Another object of the current invention is to provide aneffective apparatus for mixing and blending two or more liquidmaterials, one of which is the blowing agent and the other of which isthe polyol, to produce the blended polyol used in the manufacture ofpolyurethane foam.

Another object of the invention is to provide control of the ratio ofblowing agent to polyol by using mass flow rate measurement andelectronic control techniques. Mass flow measurement is superior tovolumetric flow measurement for the reason that due to the expansioncapacity of typical blowing agents, especially where there is not strictcontrol of pressures on the reactants throughout the system, thematerials in the system can experience substantial changes in volume.Therefore, by determining mixture component ratios based solely onvolume of flow, substantial errors in calculating the actual amount ofblowing agent will occur. Because the ratio of polyol to blowing agentis critical to the quality of foam produced, a greater degree ofprecision than that offered by prior art devices using volumetricmeasurement means is desired. The present invention provides the greaterprecision required by using mass flow measurement which avoids thepossibility of errors due to volume variations caused by changing systemdynamics (e.g. pressure or temperature).

A further object of the invention is to maintain a liquid state ofwhatever blowing agent is selected for use, and provide instantaneousblending of the ingredients in the mixture, the mixing and blending tobe accomplished on-demand requiring only one pass of the materialsthrough the system without the necessity for recirculation to a batchtank.

Another embodiment of the invention provides an apparatus suitable forprocessing a wide variety of blended polyol materials. For instance, thecurrent invention will allow selective operating pressures necessary tosatisfy the requirements of a wide variety of blowing agent and polyolcombinations. In addition, a further object of the invention is theability to control the ratio of polyol to blowing agent for the purposeof creating mixtures of reagents yielding products with variableproperties.

While not necessary to the practice of the invention, it is recognizedthat control of the temperature and pressure both immediately prior toentering the apparatus and/or immediately after exiting the apparatus ofthe present invention, may be desired to achieve satisfactory results incertain specific situations. Therefore, one embodiment of the presentinvention includes a temperature control means on the blowing agentconduit at a point just prior to the pump used to transport these agentsinto the system of this invention. The invention may also include theuse of other monitoring equipment such as temperature controllers andsight glass windows at various locations along the pathway of the systemwhich can be electronically linked to an electronic process controller.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the presentinvention will be made apparent from the following detailed descriptionof the preferred embodiment of the invention, and from the drawings, inwhich:

FIG. 1 is a schematic drawing depicting a flow chart of the apparatuscomponent parts.

DETAILED DESCRIPTION OF THE INVENTION

The present invention consists of an apparatus capable of mixing thevarious necessary components for polyurethane foam on demand by infusinga liquid state blowing agent into at least one liquid reactant atdesired temperature and pressures, and instantaneously blending theblowing agent and reactant to form a blended mixture necessary for thesubsequent formation (after introduction of a polymerizing secondreactant) of moldable foam. While it is possible to use the presentapparatus for mixing the blowing agent with either reactant, that is thepolyol or the isocyanate, it is preferred to mix the blowing agent withthe polyol to form blended polyol for the fact that some isocyanatederivatives used in the industry pose a health and safety hazard.Therefore, in the following detailed description of the preferredembodiment, it is assumed the reactant to be mixed with the blowingagent is polyol.

Referring now to FIG. 1, apparatus 1 consists of a series of conduitscapable of carrying gases or liquids under pressure. Connected in-lineto these conduits are various components of the apparatus productionsystem. It is first to be understood commensurate with ordinary skill inthe art of polyurethane foam production that the blowing agent andpolyol reactants are available from supply source vessels, blowing agentsupply 2 and polyol supply 3, and are supplied to the apparatus underknown steady state conditions. These conditions include predeterminedoperational pressures, temperatures, and flow rates in order to ensureconsistent and reliable supply of reactant materials. The exact valuesof pressure, flow rate and temperature will vary with the make up ofmaterials selected for processing. The present invention can providedesired temperature control by controlling the temperature of theblowing agent just prior to entering a motorized variable flow positivedisplacement blowing agent pump 7 by a temperature control means 16 a.It will be appreciated in the art the variety of means available formeasuring and controlling the temperature of the liquids in theapparatus. Moreover, the temperature control means may, if desired, beelectronically linked to and controlled by an electronic process orprogrammable controller 8.

Leading from blowing agent supply 2, conduit 4 is first intersected byisolation valve 5 a which may be used to start or stop the flow of theblowing agent or for isolating part of the apparatus for cleaning,inspecting or other operational function. Other isolation valves locatedwithin the system have the same purpose. Downstream of valve 5 a ispressure gage 6 a useful in determining and monitoring the pressure atwhich the blowing agent is allowed into the section of conduit 4downstream of the gage 6 a. Next in-line on conduit 4 is motorized,variable flow positive displacement blowing agent pump 7 to which isconnected pump motor M1. Variable output, positive displacement pumpingsystems are required for both the blowing agent and the polyol. Thereare many possible combinations of types of pumps which may be used, withthe primary requirement that the pump discharge rate be controllable,either manually or (as preferred) by using an electronic signal as aninput to a controlling device. Downstream of the pumps 7 and 14,measuring instruments may be placed in-line with the conduits 4 and 12to allow those parameters considered critical to the operation of theapparatus to be monitored. These are measuring devices which perform inconjunction with, or which contain, electronic devices that provideoutput signals to programmable controller 8. The programmable controller8 will interpret these signals, and monitor and control these valuesbased upon the instructions contained in the program. Parameters such aspressure, temperature, flow rate, flow volume, etc. can be monitored andor controlled. This information can also be supplied to a factoryinformation system, if one is available, which is intended to monitor orcontrol a plurality of similar conduit systems in a full-scaleproduction facility, via electronic link.

Following pump 7 is pressure gage 6 b which facilitates the accuratemonitoring of blowing agent pressure allowed downstream in the system.Following gage 6 b is isolation valve 5 b capable of restricting theflow of blowing agent, if desired for reasons discussed in conjunctionwith valve 5 a. Downstream of 5 b is blowing agent mass flow meter 9which can measure the mass flow rate of blowing agent passing throughconduit 4. The flow meter measures the mass flow rate of the dischargedblowing agent based on mass throughput (typically in pounds per minute)thereby avoiding errors and imprecision experienced with volumetricmeasuring means due to changes in volume caused by fluctuations inpressure or temperature. The value of the mass flow ratio of eachmaterial (blowing agent or polyol) will be transferred to theprogrammable controller 8 via an electronic signal. Following next isisolation valve 5 c. Next in-line is check valve 10 a to preventbackflow of mixed reactants, the check valve being placed just upstreamof a motorized kinetic blender 11. Following 10 a, conduit 4 leads intoblender 11.

Running parallel in conception to conduit 4 is polyol agent conduit 12.Conduit 12 leads from polyol supply 3 to isolation valve 5 d followed bypressure gage 6 c. Pressure gage 6 c allows the accurate measurement ofpolyol reactant pressure in the apparatus. Immediately downstream ofgage 6 c is motorized variable flow positive displacement polyol pump 14connected to pump motor M2. Downstream of pump 14 is pressure gage 6 dable to measure the pressure of polyol being pumped by pump 14 throughconduit 12. Following gage 6 d is isolation valve 5 e. Next in-line ispolyol mass flow meter 15 which is able to measure the mass flow rate ofpolyol reactant. Downstream of flow meter 15 is isolation valve 5 ffollowed next in-line by temperature control means 16 b. Downstream ofthe temperature control means 16 b is sight glass window 17 a useful forvisually monitoring flow in conduit 12. Additional sight glasses may beplaced throughout the apparatus for similar visual monitoring asdesired. Following 17 a is in-line check valve 10 b. Following 10 b,conduit 12 leads into blender 11.

Blender 11 contains a plurality of interlocking rotors having aplurality of shearing teeth capable of high speed operation. Blender 11mixes the blowing agent from conduit 4 and the polyol reactant fromconduit 12. The blending operation consists of passing the mixturethrough a device designed to intermix thoroughly any liquid materialswhich pass through it. Static or dynamic blenders may be used, althoughbetter results are obtained using a kinetic blender. Kinetic blending isthe preferred method, because the input speed of the electric motor canbe controlled, thereby giving control of the extent and degree ofblending which takes place. Blender 11 is driven by a variable speedmotor M3 and imparts kinetic energy to the fluids being blended.Subsequent to passage through the blending operation, the mixed materialis referred to as blended polyol (or blended isocyanate should it beused instead of polyol).

Downstream of blender 11 is blended reactant conduit 18 which carriesthe blended components through downstream system components. Immediatelyfollowing in-line is sight glass window 17 b. Following 17 b is blendedpolyol mass flow meter 19. One embodiment of the invention allows theblended polyol mass flow meter at this position. Another embodiment ofthe invention allows the blended polyol mass flow meter to be placeddownstream of a back pressure regulator 20. The intended purpose of massflow meter 19 is to monitor the operation of the entire system. The massflow rate measured by this meter 19 should equal the sum of the readingsof the upstream blowing agent and polyol mass flow meters 9 and 15,respectively. The readings of all three meters may be monitored by theprogrammable controller 8.

Following mass flow meter 19 is isolation valve 5 g followed by pressuregage 6 e and temperature control means 16 c. Immediately followingin-line is back pressure regulator 20. This device will maintain aselected pressure on all components upstream of its location in thesystem and downstream of the pumps 7 and 14 and is included to ensurethat low-boiling point blowing agents are processed at pressuresadequate to maintain their liquid states during processing. Next in-lineafter pressure regulator 20 is sight glass 17 c. Then, the blendedpolyol is ready for immediate use as in reacting with isocyanate to formpolyurethane or it may be stored in a day tank 21 or other storagemeans. It will be appreciated in the art that use of the method andapparatus described may require high pressure storage tank means whenlow boiling point blowing agents are used, neither of which have, asyet, been in general use in the polyurethane foam industry. Thus,retrofit of existing systems may require installation of such means.

When included in the apparatus system, the programmable controllercomputer program designates as the Primary Flow the flow of either theblowing agent or the polyol preblend (either component may be selected).The flow of the other material is designated the Secondary Flow. Aninput to the computer program from the applicable mass flow meterdesignates the rate of flow for the Primary fluid. The program containsa value referred to as a Mixture Ratio which is a preselected value(based on the characteristics of the blowing agent used and the desiredfoam qualities) which determines the ratio between the two materialsbeing pumped. The program monitors the flow rate of the Primary fluidand the Secondary fluid. The program adjusts the output of the Secondarypump so that it varies from the flow of the Primary fluid by the valueof the Mixture Ratio established in the program. This allows the ratioof one material to be controlled relative to the other. The total outputfrom the system is varied by variance of the flow rate selected for thePrimary Fluid. The Secondary Fluid will track the flow of the PrimaryFluid by the ratio determined by the Mixture Ratio. The accuracy of thecontrol is dependent upon the accuracy of the mass flow meters tomeasure the actual flow rate, and the capability of the pumping systemto control the output of each component accurately. Selection ofmeasuring and pumping devices is made based upon an evaluation of theaccuracy requirements of the system under consideration. Error messages,status reports, and emergency shutdowns can be programmed to occur underappropriate circumstances.

An example of the practice of the invention uses 1,1,1,2tetrafluoroethane (HFC-134a) as blowing agent, and polyol, both of whichare pumped by the respective variable flow positive displacement pumpsthrough the respective conduits at pressures generally of about between26 psi and 250 psi, usually at about between 70 to 150 psi, andpreferably at about between 70 to 130 psi, and at temperatures generallyof about between 30 to 145 degrees F, usually about between 70 to 10degrees F, and preferably about between 70 to 105 degrees F. The massflow meter of the blowing agent monitors the actual mass flow rate ofthe liquid blowing agent. The programmable controller signals the polyolpump motor to run at such a speed that the mass flow of polyol relativeto the mass flow of blowing agent conforms to a predetermined ratio. Theprogrammable controller makes adjustments as required to keep the ratiosof the blowing agent and polyol to the programmed levels. Generally, themass flow ratios of blowing agent to polyol are about between 5% and 40%by weight of blowing agent in the mixture, preferably about between 20%and 30% blowing agent by weight. The polyol and blowing agent are thenintroduced into the kinetic mixer and thoroughly blended at ratesgenerally at about between 300 to 3000 rpm, preferably at about between600 and 2000 rpm. The blended material is then ready for immediate useoutside the system for reacting with isocyanate and pressure reductionto induce foaming or it may be stored in a day tank or other storagemeans in the mixed, or blended, state until needed.

It will be appreciated by those skilled in the art that variousmodifications within the spirit of the invention may be made to theembodiments disclosed herein for purposes of illustration. The inventionis not to be limited to those particular embodiments, but only by thescope of the appended claims and their equivalents.

What is claimed is:
 1. An apparatus for preparing a blend of polyol anda blowing agent useful in the preparation of polyurethane type foamcomprising: a) a first and a second conduit, said first conduit havingthe capacity to channel a blowing agent under pressure sufficient tomaintain said blowing agent in a liquid state, said second conduithaving the capacity to channel said polyol under a pressure sufficientlygreat to maintain said blowing agent in a liquid state, said first andsecond conduits channeling said blowing agent and said polyol throughcomponent parts as described herein to a variable speed kinetic mixer,said mixer having at least two entrance ports and at least one exitport; b) a first and a second variable flow positive displacement pump,said first displacement pump connected in-line with said first conduit,said second displacement pump connected in-line with said secondconduit; c) a first and a second mass flow meter, said first mass flowmeter connected in-line with said first displacement pump, said secondmass flow meter connected in-line with said second displacement pump,said first and second mass flow meters further connected to saidentrance ports of said mixer via said first and second conduitsrespectively; and d) a pressure regulator means connected to said atleast one exit port of said mixer via a third conduit, said pressureregulator means having the capacity to maintain a fluid exiting saidmixer at a pressure sufficient to maintain said blowing agent in aliquid state, and said pressure regulator means further having thecapacity to control and maintain a pressure upstream to said first andsecond displacement pumps sufficient to maintain said blowing agent insaid third conduit, said mixer, and said first and second conduits anddownstream of said first and second variable displacement pumps in aliquid state.
 2. An apparatus according to claim 1 wherein said pressureregulator means is capable of maintaining a pressure within the range ofabout between 26 to 250 pounds per square inch.
 3. An apparatusaccording to claim 1 wherein said apparatus further comprises a meansfor maintaining temperature within the range of about between 30 to 145degrees F.
 4. An apparatus according to claim 1 wherein said first andsecond mass flow meters are connected to a programmable controller, saidprogrammable controller having the capacity to compare measurements fromsaid first and second mass flow meters and control the flow rate of saidblowing agent and said polyol by controlling the rate at which saidfirst and second variable flow positive displacement pumps pump saidblowing agent and said polyol, said programmable controller furtherhaving the capacity to maintain said flow rates of said blowing agentand said polyol at a ratio within the range of about between 5% to 40%by weight of blowing agent to polyol.
 5. An apparatus according to claim1 wherein no mixing tank is connected downline of said mixer.
 6. Anapparatus according to claim 1 wherein no recirculation mechanism isconnected to channel said polyol and said blowing agent through saidmixer for a subsequent mixing pass.
 7. An apparatus according to claim1, wherein said mixer has no storage capacity.